Screw-type solids discharge centrifuge having means to discharge light solids



Nov. 15, 1966 SHAPIRO 3,285,507

SCREW-TYPE SOLIDS DISCHARGE CENTRIFUGE HAVING MEANS T0 DISCHARGE LIGHTSOLIDS Filed Dec 2, 1964 INVENTOR. L LEONAR SHAPIRO BY M2;

ATTORNEY United States Patent 3,285,507 SCREW-TYPE SOLIDS DISCHARGECENTRIFUGE HAVING MEANS T0 DISCHARGE LIGHT SOLIDS Leonard Shapiro, UpperDarby, Pa., assignor to Pennsalt Chemicals Corporation, Philadelphia,Pa, a corporation of Pennsylvania Filed Dec. 2, 1964, Ser. No. 415,435 6Claims. (Cl. 233-7) This invention relates to centrifuges. Morespecifically this invention relates to a centrifuge of the solid bowltype in which means are provided to discharge separated solids from aliquid-solids mixture in which the solids are lighter than the liquid.

In the past considerable difliculty has been experienced in theseparation of light solids from the liquid phase in a liquid-solidsmixture. For instance, in separating ice solids from a brine liquid theuse of a solid bowl centrifuge has been unsatisfactory: the ice solidshave formed a solid cake and have virtually defied discharge byconventional ring dam methods. The worm-type centrifuge comprising asolid bowl having a screw conveyor moving solids toward a solidsdischarge opening has also been found useless for the separation oflight solids from a liquid-solids mixture: the light solids haveobligingly turned with the conveyor and not progressed to the discharge.

Processors have been forced in such separations to resort to screencentrifuges such a conical screens having screw conveyors, and theso-called pusher machines. Screen centrifuges have, of course, madetheir separations on the basis of particle size, and for this reason ithas been necessary to grow large crystals. The growth of large crystalsrequires exacting control, expensive and complicated chilling equipmentand a great deal of processing time. Processors have not been satisfiedwith these requirements but have accepted them as part of a Hobsonschoice.

Since the centrifugal separation of light solids which may be basedprimarily on density of the solids rather than solely on particle sizewould reduce the requirement for expensive and time-consuming crystalgrowth, the quest for a suitable solid bowl centrifuge arrangement hasbeen pursued. The present invention has for an object the provision ofsuch an arrangement.

A further object of the invention is the provision of such a machinehaving means for concentrating such light solids in unusual purity.

Additional objects and features of the invention will be apparent from astudy of the accompanying specification including drawings in which:

FIGURE 1 is a fragmentary elevation partly in section of an apparatusembodying the invention;

FIGURE 2 is a sectional View taken on the line 22 of FIGURE 1;

FIGURE 3 is a greatly enlarged schematic view showing the probableaction in an apparatus embodying the invention; and

FIGURE 4 is a sectional view taken on the line 4-4 of FIGURE 3.

Briefly, the invention is a solid bowl centrifuge in which light solidsare keyed to rotation with the centrifuge bowl and are scrolled to thesolids discharge opening by a screw conveyor extending outward into thesolids layer.

Referring more specifically to the drawings, an apparatus embodying theinvention is shown in FIGURE 1 and generally designated 10. It comprisesa frame 12 mounting a pair of pillow block bearings 14 which support thehub shafts 16 of the centrifuge bowl 18. One end of the centrifuge bowlis provided with a radially adjustable opening 20 for liquid discharge,while the other end is provided with an opening 22 for solids discharge.The wall of the bowl 18 is formed with a beach 18a inclining inwardly tothe opening 22.

A conveyor body 24 is mounted on conveyor bearings within the bowl torotate at a rate different from the speed of the bowl. The bowl 18 andthe conveyor 24 are operatively linked for differential rotation by gearbox means which is not shown but which may be disposed to the left ofthe leftward pillow block 14 as shown in FIG- URE 1. The bowl andconveyor are driven through a single pulley 32. The relation of thedriving and driven elements is as generally described in US. Patent2,703,- 766.

The conveyor body 24 is equipped with flights 26 and a rinse distributor28 including inwardly directed ribs 28a. The rinse openings 30 direct arinse liquid out into the bowl.

Means for feeding mixture to be separated into the bowl comprise a feedtube 34 which extends through the rightward hub shaft 16 as shown inFIGURE 1 and opens toward the feed passage 36. The feed passage 36conducts the feed mixture under the beach 18a and adjacent to theperiphery of the bowl. As shown in FIGURE 2 a plurality of ribs 38extend inward from the peripheral wall of the bowl 18 to a levelsubstantially equal to the level of the outer portion of the liquiddischarge opening 20. The flights 26 on the conveyor extend outward toalmost touch the inward edges of the ribs 38. Preferably the number ofribs should be great enough so that the solids may form a bridge betweenribs. This avoids circulation of liquid and solids between the ribsinduced by the relative rotation of the conveyor and bowl. Obviouslysuch circulation would be detrimental to the efficiency of theseparation.

A disc darn 40 is disposed on the conveyor body 24 ad jacent the liquiddischarge opening 20 and functions to block discharge of light solidsthrough the opening 20. To help keep the liquid between the dam 40 andthe outlet 20 rotating at the approximate speed of the bowl, radialvanes 40a may be provided on the outward face of the darn 40. This willminimize the swirling of liquid moving inward from the periphery of thedam 40 to the outlet 20 and avoid influence on the liquid level in thebowl.

Rinse liquid may be delivered to the inside of the conveyor body 24 bymeans of an inner rinse supply tube 42 concentric with the feed tube 34.The rinse liquid accelerated by the ribs 28 rotates at the speed of theconveyor and moves outward through the openings 30 to contact thesolids. For this purpose the openings 30 are concentrated in the area ofthe beach and thereadjacent.

A casing 44 is provided with suitable partition to segregate the liquidand solid discharges as is well known in the art.

In operation, a feed mixture such as a brine suspension of ice crystalsis delivered through the feed tube 34 and passages 36 into the bowl 18.The ice crystals being lighter than the brine move inward toward theliquid level "which is determined by the position of the opening 20. Theice crystals rise inwardly 0f the liquid level and form a cake (FIGURES3 and 4) inward of the ribs 38. The conveyor flights 26 scrape the topsurface of the ice cake as shown and move it toward the solids dischargeopening 22. Behind the flight 26 more ice solids push upwardly for theirengagement by the flights in turn on the next differential rotation ofthe conveyor.

It will be seen that the ribs will key the ice cake to rotation with thebowl 18 and that the differential speed of the flights 28 will result ina movement of the ice solids towards the solids discharge opening. Thesolids engaged by the flight 26 tend to turn at the speed of the bowldue to their friction with the adjacent ice held by the ribs 38.

The machine is especially effective in the separation and purificationof ice solids since the conveyor in pushing the solids toward the solidsdischarge outlet breaks up any crust of rinse liquid which coats thesolids. As a result the solids may be better permeated and contacted bythe rinse.

While a brine suspension of ice crystals has been illustratively used inthis discussion, it should be understood that the invention is adaptedfor use with many light solids; that is, many solids lighter than theliquid with which they are in admixture. As an example it iscontemplated that an apparatus embodying the invention may be used inseparating solid paraxylene from its liquid lower-melting isomers. Itsoperation in Winterizing of vegetable oils and dewaxing of petroleumoil-s by fractional crystallization is contemplated.

Variations on the structure disclosed are reasonable within the scope ofthe invention. For instance, the invention may be applied to acentrifuge having a bowl with a vertical axis such as disclosed forexample in US. Patent 3,061,181. Therefore, it is to be understood thatthe above particular description is by way of illustration and not oflimitationyand that changes, omissions, additions, substitutions, and/orother modifications may be made without departing from the spirit of theinvention. Accordingly, it is intended that the patent shall cover, bysuitable expression in the claims, the various features of patentablenovelty that reside in the invention.

I claim:

1. A centrifuge comprising a solid bowl having discharge openings atopposite ends for liquid and solids, respectively, the liquid dischargeopening being disposed at a level spaced inward from the periphery ofthe bowl, the solids discharge opening being spaced inward from theliquid discharge opening, a screw conveyor within the bowl for movingsolids to the solids discharge opening, flights on the screw conveyorextending outward to a level in the bowl just inward of thefirst-mentioned level, and ribs secured to the periphery of the bowl andextending inward approximately to said first-mentioned level along asubstantial portion of their length.

2. A centrifuge as described in claim 1 wherein the wall of the bowl isformed with a beach portion extending from the outer periphery of thebowl to the solids discharge opening.

3. A centrifuge as described in claim 2 wherein feed is delivered to thebowl through a passage which extends outward of the inner surface of thebeach portion and terminates in a discharge opening adjacent theperiphery of the bowl.

4. A centrifuge comprising a solid bowl having a solids dischargeopening, and a liquid discharge opening actward from the solidsdischarge opening, a screw conveyor in the bowl having flights formoving solids to the solids-discharge opening and a plurality of ribsextending inward from the bowl wall to the radius of theliquid dischargeopening for substantially the entire lengthof the bowl, the conveyorflights extending out to the level.

5. A centrifuge comp-rising (a) a solid bowl having substantiallylongitudinal ribs extending inward to a first radius along a substantialportion of their length,

(b) a conveyor disposed coaxial with and inside the bowl and havingflights extending out to the first radius,

(0) the bowl having a liquid discharge port at the first radius, and

(d) the bowl having a solids discharge port inward from the firstradius.

6. The method of separating light solids from mixture with a heavierliquid which comprises introducing the mixture to a zone ofcentri-fugation wherein the solids float to a layer inward of theliquid, keying the floating solids layer to rotation with the bowl, andengaging solids in the layer with a spiral conveying surface rotatingrelative to the bowl to move the solids inward to a solids dischargeopening.

References Cited by the Applicant UNITED STATES PATENTS 1,06 4,1846/1913 Wels. 2,573,585 10/1951 McBean. 3,228,593 1/1966 Topping.

M. CARY NELSON, Primary Examiner. H. T. KLINKSIEK, Assistant Examiner.

1. A CENTRIFUGE COMPRISING A SOLID BOWL HAVING DISCHARGE OPENINGS ATOPPOSITE ENDS FOR LIQUID AND SOLIDS, RESPECTIVELY, THE LIQUID DISCHARGEOPENING BEING DISPOSED AT A LEVEL SPACED INWARD FROM THE PERIPHERY OFTHE BOWL, THE SOLIDS DISCHARGE OPENING BEING SPACED INWARD FROM THELIQUID DISCHARGE OPENING, A SCREW CONVEYOR WITHIN THE BOWL FOR MOVINGSOLIDS TO THE SOLIDS DISCHARGE OPENING, FLIGHTS ON THE SCREW CONVEYOREXTENDING OUTWARD TO A LEVEL IN THE BOWL JUST INWARD OF THEFIRST-MENTIONED LEVEL, AND RIBS SECURED TO THE PERIPHERY OF THE BOWL ANDEXTENDING INWARD APPROXIMATELY TO SAID FIRST-MENTIONED LEVEL ALONG ASUBSTANTIAL PORTION OF THEIR LENGTH.